Objects which are submerged in water, such as ship hulls and anchored structures, are prime targets for undesired marine growth accumulation because many marine organisms require permanent attachment to a solid object. Such accumulation and eventual encrusting can promote corrosion and interfere with the normal workings of submerged structures. To prevent such fouling, antifouling paints containing various biotoxins have been used to coat submerged structures. Biotoxin-loaded paints prevent fouling by interfering with the ability of marine organisms to attach to submerged structures, either by weakening or killing the organism.
Typical antifouling paints contain one or more marine biotoxins contained in a resin. To achieve a lethal concentration of biotoxin at the water-substrate interface, such paints rely on diffusion of biotoxin through the resin to the paint surface. Because the rate of diffusion of biotoxin from the surface into the water is much faster than the rate of diffusion of biotoxin from the bulk resin to the surface, the surface concentration of biotoxin drops below the lethal limit long before all of the biotoxin in the paint is depleted. Both material and time (i.e., that necessary to repaint the substrate) are wasted through this inefficient method.
Recent advances in this area include erodible, or "self-polishing", paints. With such paints, a fresh surface of paint, and thus of biotoxin, is continuously exposed through the slow dissolution or disintegration of the outer layer of paint into the surrounding water. Significant amounts of water-eroded polymer are left to pollute the water body in question, however.
Alternative antifouling materials have been developed. For instance, marine organisms can be removed (e.g., by high pressure sprays) from surfaces treated with release coatings, such as silicones and fluorinated epoxy polymers, more easily than from non-treated surfaces. A similar approach is to bond a sheet containing such a coating to the marine surface through an intermediate barrier layer. A copper-nickel alloy plate with a primer layer and an adhesive is described in U.S. Pat. No. 4,814,227. Another alternative, described in U.S. Pat. No. 4,865,909, is a hydrophobic polymeric membrane, containing numerous pores, which is adhered to the surface to be protected by a biotoxin-containing paint. Here, the paint is still the antifouling agent, but the membrane prevents random leaching of the active agent into the surrounding water. The preferred polymeric substance for this method is polytetrafluoroethylene (PTFE).
Particle-loaded, non-woven, fibrous articles wherein the non-woven fibrous web can be compressed, fused, melt-extruded, air-laid, spunbonded, mechanically pressed, or derived from from phase separation processes have been disclosed as useful in separation science. Sheet products of non-woven webs having dispersed therein sorbent particulate have been disclosed to be useful as, for example, respirators, protective garments, fluid-retaining articles, wipes for oil and/or water, and chromatographic and separation articles. Coated, inorganic oxide particles have also been enmeshed in such webs. Such webs with enmeshed particles which are covalently reactive with ligands (including biologically-active materials) have also been recently developed.
Numerous examples of PTFE filled with or entrapping particulate material are known in many fields. Many applications for PTFE filled with electroconductive materials are known. These include circuit boards, oil leak sensors, electrical insulators, semipermeable membranes, and various types of electrodes. Other such combinations have been used as gasket or sealing materials and wet friction materials. Still others have been used to produce high-strength PTFE films and sheets with applications as structural elements and electronic components. Where the particulate has catalytic properties, this type of combination provides a form which can be conveniently handled. U.S. Pat. No. 4,153,661 discloses various particulate, including cupric oxide, distributed in a matrix of entangled PTFE fibrils as being useful in, among other things, electronic insulators and semipermeable membranes.
Numerous combinations of PTFE and metals in which the metal is not entrapped within a PTFE matrix are also known. These include PTFE membranes completely or partially coated with metal and metal matrices with a network of fibrillated PTFE in the pores thereof. PTFE powder with metal filler has been used (in paste form) as a battery electrode and as a self-lubricating layer coated on bronze bearings. PTFE films coated onto metal films and plates are also known.
Methods of preparing fibrillated PTFE webs have been described in, for example, U.S. Pat. Nos. 4,153,661, 4,460,642, and 5,071,610.